The present invention relates to techniques for performing wellbore operations. More particularly, the present invention relates to techniques for determining characteristics of subterranean formations.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions.
Oil rigs are positioned at wellsites for performing a variety of oilfield operations, such as drilling a wellbore, performing downhole testing, and/or producing located hydrocarbons. To produce hydrocarbons economically, an accurate estimation of hydrocarbon volume may be performed. Conventional resistivity interpretation techniques may be less reliable in the presence of clays, which often increase formation conductivity and may mask the presence of hydrocarbons.
Several physical models have been developed to address the influence of clays on the physical properties of formations, and to accurately determine hydrocarbon volume from resistivity measurements. For example, the Waxman-Smits and Dual-Water models have been used in the oilfield industry. However, conventional models may be affected by various uncertainties and inaccuracies of what is known of the formation. For example, the Waxman-Smits model uses an external input of the formation Qv (the Cation Exchange Capacity per unit pore volume). However, the Cation Exchange Capacity (CEC) is often inferred from indirect formation lithology or lab measurements which may be affected by uncertainties in determination of the formation lithology and clay type. Alternative techniques of measuring the CEC in a lab uses well coring, which can be relatively time consuming.